This invention relates to the field of cardiovascular medicine and whole body medicine and consists of a new system and device for assessing cardiovascular function in which arterial distensibility and stiffness is determined from pulse wave velocity, and method thereof.
Cardiovascular disease is a leading cause of morbidity and mortality in most industrialized nations. Large-artery pathology is the major contributor to cardiovascular disease. Changes to the arterial wall are usually associated with age, smoking, diabetes, dyslipidemia, hypertension, and other known factors. Thus, arteries constitute the target site and the common denominator of cardiovascular risk factor complications.
Most noninvasive methods for assessing the condition of large arteries are costly and generally are within the purview of only a limited number of clinical research laboratories. In a more typical clinical setting, simpler methods are required for large-artery assessment. Arterial pulse wave velocity is a simple, noninvasive, accurate, and reproducible method for assessing arterial stiffness and distensibility. Pulse wave velocity is related to the geometry, the structure, and the function of the arterial wall. The arterial pulse is a fluctuation caused by heart contraction and occurs at the same frequency as the heart rate. The ejection of blood from the left ventricle through the aortic valve in the aorta leads to flow, pressure, and diameter pulsations throughout the arterial tree.
The basic principle behind arterial pulse wave velocity measurement is that the pulse wave generated by left ventricular ejection is propagated along the arterial tree at a speed determined by the elastic and geometric properties of the arterial wall, and by blood density. The material properties of the arterial wall, its thickness, the lumen diameter, and factors such as age and blood pressure levels, among others, are considered to be the major determinants of pulse wave velocity. Measurement of the pulse wave velocity is based on the determination of the time delay between two pulse waves recorded at two distinct sites along the arterial system, using a separate specific transducer at each site. The distance traveled by the pulse wave is obtained from measurements of the distance between the two recording sites. Pulse wave velocity is calculated from measurements of the pulse transit time and the distance traveled by the pulse between the two recording sites.
The determination of the time delay between the pressure waves, recorded at two distinct points of the arterial system, is currently performed using continuous recordings of the pressure curves traces generated by the pulse wave. These recorded curves represent the typical pressure wave peaks corresponding to a single heart-beat. To determine the transit time using this method, the time delay between the two maximal peaks of the pressure wave corresponding to the same pulse is calculated. This interval can be obtained by direct measurement from the printed curve traces of the two recordings. However, maximal peak determinations are variable, depending on several clinical and biological parameters such as gender, height, weight, heart rate, pulse wave reflection, and age. Thus, the precision of the time interval determination may be poor and may limit the overall quality of the measurement using previously known methods and devices to measure pulse wave velocity.
The present invention provides a system, device, and noninvasive method for the automatic determination of the pulse wave transit time between two recording sites (M1, M2) in a mammalian arterial system, according to a procedure that involves the following stages:
a) Application of a pressure-sensitive transducer at each recording site of the arterial system.
b) Recording of the pulse wave at each of the two recording points.
c) Calculation of the pulse wave time interval between the two recording sites as follows:
c1) At the first recording site, the determination on the proximal waveform of the time t1 by identifying the foot of the wave at the beginning of the initial upstroke.
c2) At the second recording site, the determination on the distal waveform of the time t2 corresponding to the same pulse wave by identifying of the foot of the wave.
c3) Determination of the transit time from the time delay between the two corresponding waveforms, the proximal (t1) and the distal (t2) pulse waveforms.
In addition, the current invention allows the calculation of the pulse wave velocity between the two recording sites and the evaluation of the aortic pulse pressure from the previously determined pulse wave velocity.